The present invention relates to certain polyester polyols suitable for blending with propoxylated polyether polyols or other materials mutually compatible with foam blowing agents and polyester polyols to achieve polyisocyanurate foams of excellent dimensional strength and acceptable levels of fire resistance, and a method for making them.
The use of polyester polyols to prepare urethane foams is an old and well-known procedure. Over the years many inventions have been made to improve the resultant products in terms of lower costs, lower viscosity to permit ready handling in conventional urethane mixing and pumping systems, better dimensional strength of the foam, increased fire retardancy of the foam, and many other properties.
Many attempts have been made to use polyester polyols, such as the Hercules "Terate" products, in a blend with propoxylated polyether polyols to achieve the ASTM E 84 Class 2 fire resistance rating without fire retardants, or the Class 1 fire resistance rating upon addition of fire retardants such as tri(B-chloroisopropyl) phosphate. Other polyester/polyether polyol blends have been attempted to commercially utilize polyester polyol products, but have suffered from problems such as a high viscosity which hinders mixing, inadequate fire resistance due to the presence of a high hydrogen content, a polyol B blend which separates or contains solids such that settling and storage tank build-up and strainer plugging problems occur, a high hydroxyl number such that sufficient trimerized polyisocyanurate stabilizing rings cannot be formed without using large proportions of polymeric polymethylene polyphenyl isocyanate (PMDI) and thus substantially increasing the total cost, or the cost of the polyester polyol is too high to be of commercial value.
In an effort to reduce costs, many attempts have been made to use "bottoms" or "side streams" from major processes, and also to re-use plastic waste or scrap. For example, U.S. Pat. No. 3,647,759 teaches the use of side streams from a DMT production process as a source of aromatic core units for polyester polyols going into polyurethane foams. Also, the reduction by alcoholysis and glycolysis of high molecular weight polyethylene terephthalate plastic waste or scrap into low molecular weight oligimers is an old and wellknown art, as set forth as early as 1966 by H. B. Whitfield, Jr., et al. in U.S. Pat. No. 3,257,335 (now expired), plus several others, including Ooba, et al. (U.S. Pat. No. 3,857,799), H. S. Ostrowski (U.S. Pat. No. 3,884,850), Currie (U.S. Pat. No. 3,907,868), and Svoboda (U.S. Pat. No. 4,048,104), all of whom teach using diols to digest PET. The prior art does not teach making a diol oligimer from PET by substituting a majority of the ethylene glycol produced in PET digestion with a higher boiling point diol. It has been found that if no ethylene glycol is removed, thus leaving equal molar amounts of phthalate core units to ethylene glycol units, a copolyester polyol cannot be made which has a sufficiently low level of all three (3) of the following properties concurrently:
(1) A low enough hydroxyl number to produce a PIR foam with a -NCO to -OH ratio high enough to make a stable foam and still reduce PMDI costs; and PA1 (2) A viscosity low enough to provide good mixing, good spreading, and good handling operability; and PA1 (3) A hydrogen content low enough to provide sufficient fire resistance to achieve Class 1 and more severe fire tests. PA1 1. an aromatic component selected from phthalic anhydride; phthalic acid isomers; phthalic acid halide isomers; di-lower alkanol esters of phthalic acid isomers; digestion products of polyethylene terephthalate; or mixtures thereof; and PA1 2. at least one aliphatic component selected from succinic anhydride; succinic, glutaric, or adipic acids; di-lower alkanol esters of succinic, glutaric, or adipic acids; acid halides of succinic, glutaric or adipic acids; or mixtures thereof; and PA1 3. at least one primary hydroxyl glycol; and PA1 4. at least one secondary hydroxyl glycol; the mole ratios of the components being: PA1 A. from about 30 percent up to about 90 percent by weight of the above hydroxyl terminated copolyester polyol resin, and PA1 B. from about 10 percent up to about 70 percent by weight of any materials or blends of materials which are mutually compatible with blowing agents and said polyester polyols, wherein the final blend will provide sufficient urethane cross-linking functionalities or allow isocyanate trimerization to produce dimensionally stable foams. PA1 (a) polymeric polymethylene polyphenyl isocyanate; PA1 (b) the polyol blend prepared as above; PA1 (c) catalysts suitable for preparing a polyurethane and a polyisocyanurate foam; PA1 (d) a blowing agent suitable for preparing a polyurethane modified polyisocyanurate low density foam; and, optionally, PA1 (e) a silicone surfactant suitable for controlling foam cell size and shape. PA1 (a) glycols to aromatic plus aliphatic component in the range of 1.3 to 2:1; preferably 1.5 to 1.6:1; PA1 (b) aromatic component to aliphatic component in the range of 0.6 to 4.0:1; preferably 1.0 to 2.5:1; PA1 (c) a secondary to primary hydroxyl glycol of from 0.05 to 0.4:1; preferably 0.1 to 0.4:1; and PA1 (d) ethylene glycol content to aromatic component of from about 0.01 to 0.5:1.0; preferably 0.06 to 0.4:1.0.
For example, with some low molecular weight polyols which have an adequate low viscosity, it has been found that they oftentimes have a high hydrogen content which produces poor fire retardancy or a hydroxyl number so high as to require a large proportion of isocyanate to form a suitable foam, thereby greatly adding to cost. Because of a low proportion of polyol, the blowing agent; such as CFC-11 must be blended into the isocyanate into an "A" blend portion as it is conventionally called. This imbalance precludes the use of normal urethane mixing equipment and creates mixing problems.
Efforts to use polyester polyols which are predominantly diols to make urethane foams lacking isocyanurate linkages have been restricted by the low levels of diol which can be tolerated. For example, in U.S. Pat. No. 4,223,068, a maximum of 30 weight percent diol could be used in a mixture with higher functionality polyols to form a polyurethane foam. The fire resistance and dimensional stability in this patented foam were not obtained from trimerized polyisocyanurate. Further, the polyurethane foam prepared does not necessarily require a secondary glycol or an aliphatic core component. U.S. Pat. No. 4,417,001 discloses the use of a secondary hydroxyl glycol, dipropylene glycol (DPG), in order to introduce blowing agent miscibility. In addition to adding compatibility, DPG also adds equivalent weight which reduces the hydroxyl number. Together these properties make it possible to use a higher percentage of the copolyester polyol in a B blend formulation; however, this copolyester polyol has a hydrogen content so high it cannot be used in large quantities alone to achieve a Class 2 foam or with fire retardants to achieve Class 1. Thus, we see that the failure to remove a majority of the ethylene glycol content produced by the disassociation (digestion) of PET has required a large amount of secondary glycol to compensate for the negative effects of ethylene glycol, and has been detrimental to this polyol. The polyol of the present invention requires that at least 50% of the ethylene glycol produced in the digestion of PET be removed prior to use, and, further, that a minimum of secondary hydroxyl glycols be present and also that aliphatic acid core components must be used, as well as primary hydroxyl glycols and an aromatic core unit. These requirements provide the polyol with a low enough hydroxyl number and enough blowing agent miscibility such that up to 90% (by weight) of a polyol blend can be the polyester which in turn provides the highly trimerized polyisocyanurate foam with good dimensional stability and fire resistance.
In U.S. Pat. No. 4,400,477 polyester polyols are disclosed which eliminate some of these previous problems, such as the need to add fire retardants to achieve ASTM E 84 Class 1 flame spread rating. Also, these polyols do not require additional materials in order to obtain complete CFC-11 miscibility. However, these polyols are not entirely satisfactory for all types of applications. For example, these polyols have a limited range of reaction speeds when reacting with PMDI. Many foam applications require that reaction speeds be much slower or faster than can be achieved with these polyols. Also, no provision was made for a polyol blend (or B blend) containing higher functionality groups, which omission correlates to a lack of "green strength", thus requiring careful handling in the demolding process. Many foam applications require that products be demolded quickly. Further, many foam applications do not require the Class 1 flame spread rating of these polyols. For example, some insulation used in the construction industry may only require a moderate level of fire resistance with a flame spread between 25 and 75.
Thus, while some success has been encountered in one or more of the desired properties, it has not been possible to have polyol blends with the requisite low viscosity, a low percent hydrogen content for good flame resistance, a moderate level of CFC-11 miscibility, a high degree of early green strength whereby products are more easily demolded, a low enough hydroxyl number to allow for adequate formation of polyisocyanurate rings at moderate levels of PMDI addition, and the capability of a broad range of reaction speeds when reacting with PMDI.